Process and apparatus for removing metallic ions from an electrolytic solution

ABSTRACT

The present invention relates in general to a new and improved process and apparatus for removing metallic ions from an electrolytic solution, and it relates more particularly to a process and apparatus which may be used to economically purify an electrolytic solution containing only minute amounts of metallic ions. Those knowledgable in the metal plating art will readily understand the application of this process and apparatus for the final treatment of metal finishing waste fluids. As is explained more fully hereinafter, the process and apparatus of the present invention is also effective in removing organic compounds and phosphates from the electrolytic solution under treatment.

This is a division of Application Ser. No. 445,544 filed Feb. 25, 1974now U.S. Pat. No. 3,896,013.

BACKGROUND OF THE INVENTION

Purification of metal hydroxide solutions by means of electrolysiswherein the metallic ions are removed from the solution and deposited ona porous carbon electrode is described in U.S. Pat. No. 3,459,646. Inthat prior art system, the cathode is a porous block of carbon orgraphite supported across a liquid flow path and through which theelectrolytic solution to be treated is passed. An anode electrode ismounted in proximity to either the upstream or downstream side of thecathode to develop a steady DC electric field between the anode andcathode whereby to cause the metallic ions in the solution passingthrough the pores in the cathode to separate out of solution and beplated onto the interior surfaces of the carbon electrode. After thepores have become substantially plugged by the deposited ions it isnecessary to interupt the operation and remove the metallic ions fromthe pores of the carbon electrodes by, for example, reversing thepolarity of the system, chemically treating the carbon electrode with anacid solution or replacing the carbon electrode. The down time of thesystem is, therefore, substantial whereby two such systems would berequired for each overall purifying system with which this process is tobe employed.

Moreover, when this prior art electrolytic metal removal system is to beused in the metal plating industry to purify plating solutions prior toemission thereof to the local sewer system or nearby stream, it is stillnecessry to remove other objectionable materials from the platingeffluent by other means. Such objectionable materials commonly found insuch solutions are phosphates and organic molecules and compounds.Additional equipment is thus necessary for this additional purification.

SUMMARY OF THE INVENTION

Briefly, the process and apparatus of the present invention employs aporous cathode electrode made up of fine powder carbon particles held inthe form of a porous cake on the upstream side of perforate substrate bythe pressure of the electrolytic solution being forced through the cakeand the substrate. The cake is initially formed in much the same way aprefilt cake is deposited on a perforated filter element in a pressurefilter, and as the electrolysis process is continued, additionalpowdered carbon is fed into the solution upstream of the cake wherebyfresh carbon particles are added to the surface of the cake as theprocess proceeds. By using activated carbon, phosphates and organicmolecules may also be separated from the solution and deposited on theinterstitial surfaces of the powdered carbon cake simultaneously withthe deposition of the metallic ions thereon. Periodically or wheneverthe cake is so thick as to impair the operation of the system, thesystem is shut down; the cake is physically removed from the substrateby any of the ways well known in the filter art for removing filter cakefor filter leaves or tubes; another carbon cake is then deposited on thesubstrate; and the apparatus is thereafter returned on line. At thepresent time the low cost of powdered carbon makes it uneconomical torecover values from the used cake unless the metal removed from solutionis particularly valuable. However, in such a case recovery is easilyaccomplished by heating the used carbon in a kiln to burn off thecarbon, leaving the metal as a residue.

BRIEF DESCRIPTION OF THE DRAWING

Further objects and advantages and a better understanding of the presentinvention can be had by reference to the following detailed description,wherein;

FIG. 1 is a partially schematic, vertical cross-sectional view of metalion removing apparatus embodying the present invention; and

FIG. 2 is a cross-sectional view of a cathode leaf on which a carbonpowder cake is deposited.

Referring to the drawing, a pressure tank 10 is provided with aremovable cover 11 having an inlet port 12 therein, and a large bottomopening closed by a removable bottom cover 14. An outlet manifold 15extends diametrically across the tank near the bottom and provides atone end the effluent outlet 16 outside the tank. The manifold 15 iswelded to the tank 10 to hold it in position therein.

Mounted within the tank on the manifold 15 are a plurality of hollowpressure leaves 18 having perforate facial surfaces and having internalrecesses communicating with the outlet manifold 15 through tubularconnections 20 at the bottom. The leafs 18 include a metal frame 18a, acourse wire grid 18b and wire screens 18c rivetted to the frame. Afabric bag 23 overlies the frame and screens and is suitably tied to theconnectors at the top and bottom. Extending across the tops of theleaves 18 is a metal bar 19 which is secured as by bolts or othersuitable means to the leaves 18. The bar 19 extends through an electricinsulator and pressure seal 21 to the outside of the tank where it isconnected to an impactor type vibrator 22. As explained more fullyhereinafter, the metal leaf frame is at the same electric potential asthe bar 19. The connectors 20 are suitable electric insulators such asplastic tubes whereby the leaves 18 are insulated from the tank 10.

A pluarality of wire mesh planar grids 24 are mounted between the bar 19and the outlet manifold 15 in spaced parallel relationship to the facesof the leaves 18 as shown. The grids 24 are supported within metalframes 26 having essentially the same shape as the peripheral portionsof the leaf frames. The grid frames are mounted to the bar 19 byinsulating connectors 28 and to the manifold 15 by metal connectors 30.Accordingly the grids are at the same electric potential as the tank andthe outlet manifold and thus at ground potential in a normalinstallation.

A source ofDC voltage such as the illustrated DC generator 31 or othersuitable source supplies a DC voltage for developing a DC electric fieldbetween the grids 24 and the leaves 18. The connectors to the generatorare polarized such that the grids 24 are at a positive electricpotential relative to the leaves 18. Preferably, the fine mesh wovenfabric bag 23 is itself electrically conductive being woven, forexample, of carbon filled filaments.

In operation, carbon powder is mixed with a liquid and supplied underpressure to the tank 10 through the inlet 12. The entrained carbonparticles being larger than the interstices in the leaves 18 aredeposited on the faces thereof in the form of porous carbon cakes 31 andthe clarified liquid passes out of the filter via the effluent outletmanifold 15. During the initial buildup of the carbon cakes on the facesof the leaves 18 the liquid may be recirculated from the outlet 16 tothe inlet while carbon powder is body fed into the recirculation line.After the cakes are thus built up to a sufficient minimum thickness ofabout three quarters of an inch; the generator 32 is energized wherebythe grids 24 become anodes and the carbon cakes 31 become cathodes. Thesystem is then placed on stream whereby the liquid from which the metalions are to be removed enters the tank thru the inlet 12 and exitsthrough the manifold 15. The metal ions are thus deposited on theexposed surfaces of the carbon particles in the same manner well knownin the art of electrolytic ion removal. Moreover, by using steamactivated carbon powder, organic compounds and phosphates contained inthe liquid are adsorbed by the carbon particles in the cakes during themetal removal process.

In order to permit extended operating cycles, carbon powder is body fedto the liquid being purified before it enters the tank 12 whereby freshcarbon particles are deposited on the outer surfaces of the cakes. Sincethe distances between the anode screens and the carbon cakes thusdecrease during the operating cycle, there is provided in accordancewith another feature of the present invention, control means for varyingthe negative voltage on the leaves as the purification cycle proceeds.As shown for illustration purposes only, this control means employs apotentiometer 33 having a wiper 34 driven by a timer motor 35. Duringthe metal removal operation the wiper is moved upwardly, as shown,thereby to gradually decrease the voltage between the carbon cakes andthe anode screens as the cycle progresses.

There is thus provided a new and improved electrolytic process andapparatus for continually building up carbon electrodes during a metalion removal operaton. The invention is described in connection withgenerally planar surfaces on which the carbon cakes are built up but itwill be understood by those skilled in the art that perforate tubessurrounded by hollow cylindrically shaped anodes may also be used tocarry out the process of the present invention whereby the carbonelectrodes will be hollow cylinders disposed within the cylindricalanodes.

What is claimed is:
 1. Liquid treating apparatus for removing metal ionsfrom a liquid solution, comprisingtank means having a pressure chambertherein, a first member having a cavity therein and mounted in saidchamber, said first member having a foraminous outer surface separatingsaid cavity from said chamber, a porous cake of carbon particlesdeposited on the outside of said foraminous surface, a second membermounted in said chamber in spaced relationship with said cake, means formaintaining a potential difference between said members to establish anelectric field through said cake, a liquid inlet through which saidliquid solution is supplied to said chamber, and a liquid outletconnected to said cavity for carrying the treated liquid from said tank,whereby as said liquid passes through said cake into said cavity metalions are deposited on the interior surfaces of said cake.
 2. Apparatusaccording to claim 1 wherein said first member comprisesa leaf havingoppositely disposed foraminous faces on which said carbon particles aredeposited to form said cake.
 3. Apparatus according to claim 1whereinsaid first member is conductive and electrically insulated fromsaid tank.
 4. Apparatus according to claim 1 wherein said means formaintaining a potential difference comprisesmeans having a variableoutput voltage, and means for causing said output voltage to decreaseand maintain a constant electric field intensity between said secondmember and said cake as the thickness of said cake increases duringoperation of said apparatus.